Scott H L, McCullough W S
Department of Physics, Oklahoma State University, Stillwater 74078-0444.
Biophys J. 1993 May;64(5):1398-404. doi: 10.1016/S0006-3495(93)81506-6.
We describe a statistical mechanical model for lipid-cholesterol mixtures in the P beta' (ripple) phase of lipid bilayers. The model is a simple extension of an earlier model for the ripple phase in pure lipid bilayers. The extension consists of adding a degree of freedom to allow for the occupation of underlying lattice sites by cholesterol molecules, and adding a lipid-cholesterol interaction term to the model Hamiltonian. The interaction term was constructed based on numerical calculations of lipid-cholesterol energies for several different packing juxtapositions of the two molecules. Other than the lipid-cholesterol interactions, the extended model uses the same parameter set as the earlier model, so that comparison of the properties of the extended model with experimental data serves as a test of the validity of the original model. Properties of the model were calculated using the Monte Carlo method. Results are displayed as snapshots of the ripple configurations at different cholesterol concentrations. The spacing of the ripples increases with increasing cholesterol concentration and the rate of increase compares very well with experimental data. The success of this model supports the conclusion drawn earlier that frustration arising from anisotropic packing interactions is responsible for the ripple phase in lipid bilayers. In the extended model these packing interactions are responsible for the selective partitioning of cholesterol in the regions between the ripples.
我们描述了一种用于脂质双层Pβ'（波纹）相脂质 - 胆固醇混合物的统计力学模型。该模型是早期纯脂质双层波纹相模型的简单扩展。扩展内容包括增加一个自由度，以允许胆固醇分子占据底层晶格位点，并在模型哈密顿量中添加脂质 - 胆固醇相互作用项。相互作用项是基于对两种分子几种不同堆积并列情况下脂质 - 胆固醇能量的数值计算构建的。除了脂质 - 胆固醇相互作用外，扩展模型使用与早期模型相同的参数集，因此将扩展模型的性质与实验数据进行比较可作为对原始模型有效性的检验。使用蒙特卡罗方法计算模型的性质。结果以不同胆固醇浓度下波纹构型的快照形式展示。波纹的间距随胆固醇浓度增加而增大，其增加速率与实验数据非常吻合。该模型的成功支持了早期得出的结论，即各向异性堆积相互作用产生的受挫效应是脂质双层中波纹相的原因。在扩展模型中，这些堆积相互作用导致胆固醇在波纹之间的区域选择性分配。
